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The details of predicting the aerodynamic forces of maneuvering helicopter rotors are discussed in this paper. A new approach to modeling the unsteady rotor aerodynamic forces is presented based on the insight into nonuniform induced velocity distribution, inflow dynamics and unsteady airfoil behavior. For a specified maneuver, the rotor control inputs and helicopter flight attitudes during the maneuvering are first obtained using inverse solution technique, and then the unsteady rotor forces are numerically simulated by synthetically applying the vortex theory, dynamic inflow theory and unsteady airfoil aerodynamic models. Good results of the sample calculations of lateral jink and pop‐up maneuvers are obtained.

An analytical method to predict the effects of rotor downwash on engine jet was proposed to investigate the flow pattern of helicopter engine jet. First, free wake analysis was carried out to calculate the rotor wake geometry and the downwash around the engine jet space. Then the engine jet path, cross section shape and physical variants were calculated and analyzed. Finally, an example was given to show the typical results for an insight into the influence of engine jet upon the temperature distribution around a helicopter. The method developed here can be used to predict rotor wake, engine jet and temperature distribution of a helicopter.

The sandy environment is one of the typical environments in which helicopters operate. Air-sand two-phase flow in sandy environments may be an important factor affecting flight safety. Taking a typical example, this paper aims to investigate the aerodynamic and rotor trim characteristics of the UH-60 helicopter in sandy environments.

A computational study is conducted to simulate the air-sand flow over airfoils based on the Euler–Lagrange framework. The simulation uses the S-A turbulence model and the two-way momentum coupling methodology. Additionally, the trim characteristics of the UH-60 rotor are calculated based on the isolated rotor trim algorithm.

The simulation results show that air-sand flow significantly affects the aerodynamic characteristics of the SC1095 airfoil and the SC1094R8 airfoil. The presence of sand particles leads to a decrease in lift and an increase in drag. The calculation results of the UH-60 helicopter rotor indicate that the thrust decreases and the torque increases in the sandy environment. To maintain a steady forward flight in sandy environments, it is necessary to increase the collective pitch and the longitudinal cyclic pitch.

In this paper, the aerodynamic characteristics of airfoils and the trim characteristics in the air-sand flow of the UH-60 helicopter are discussed, which might be a new view to analyse the impact of sandy environments on helicopter safety and manoeuvring.

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized wake model, a semi‐empirical correction for the vortex core effect on rotor wake is made and free wake calculation is carried out. As an example of its engineering application, the calculated downwash velocity field along the rocket launch line is presented and simply analysed. In terms of theory, the method developed here may provide of a referable basis for further study the formation mode of the tip vortex and vortex core interior structure.

As compared with the maneuvering flight studies for single main rotor helicopters, the corresponding studies for coaxial rotor helicopters are relatively poor. In this paper, the maneuvering flight governing equations for coaxial rotor helicopters is established. By introducing induced velocity interference factor analysis, the coaxial rotor aerodynamic interference can be taken into account. With the combination of coaxial rotor helicopter control features and nonlinear inverse simulation technique, the governing equations for maneuvering flight can be solved so as to determine helicopter control input, control force and moment, and helicopter body attitudes which are needed for performing a specified maneuver. Good results of the sample calculations of level turn and lateral jink maneuvers are obtained and simply analyzed.

To establish a method for the calculations in the field of rotor aerodynamics.Design/methodology/approach – The calculations of the lift‐drag characteristics of OAF and NACA63A312 airfoils at low speed are made using Jameson/TVD mixed scheme. By means of finite volume approach for numerical discretization and Runge‐Kutta time‐stepping advance, Euler/Navier‐Stokes equations are solved. Furthermore, a model based on circular tiny segment momentum theory and blade element theory is established to study the thrust and power of ducted tail rotor.Findings – The results of the calculation demonstrate the feasibility of the established method for analyzing ducted tail rotor aerodynamic characteristics.Research limitations/implications – Although the global thrust and power of ducted tail‐rotor could be obtained using current method, the exact flow filed (such as shroud pressure field and the flow over fan blade) calculations still rely on the complex three‐dimensional CFD technique that should be studied in future.Practical implications – A very useful method for the preliminary design of the ducted tail rotor.Originality/value – By comparing the calculated results with those of relevant experiment, it is proved that the method developed here is suitable for the calculations in the field of rotor aerodynamics.

This paper describes the typical maneuvering courses of helicopters with mathematics systematically and presents the formulas and approaches for calculating the dynamics characteristics. A set of generalized equations which govern the kinematics and dynamics of helicopters in maneuvering flight is given. Three aerobatic maneuvers for loop, roll and turn are specially analyzed in detail and the sample calculations are presented. The method established in this paper is of practical significance for aerobatic employment and design of helicopters.

This paper aims to present a theoretical method for analyzing the stability and control of a hingeless helicopter in the presence of windshear.

In this paper, the stability and control of a hingeless helicopter in the presence of windshear are investigated. First, the rotary wing dynamic model considered is the one of flap‐pitch (including the elastic deformation of the control system)‐torsion coupling. The induced velocity nonuniform distribution derived from vortex theory is taken into account. Then, as for atmospheric turbulence, the linear windshear model is used for modeling the variation of wind field. Finally, according to the calculated results of the stability characteristic roots and the control response of the helicopter, the helicopter performance in wind shear field is analyzed, and some conclusions are obtained.

Some useful conclusions are obtained through sample analysis.

Although the analyses for stability and control of a hingeless helicopter in the presence of windshear could be obtained using the current method, the model of complex wind field will still be expected in future studies.

A very useful method for analyzing helicopter stability and control.

The proposed method is valid and available for the analysis of helicopter flight dynamics.

Labyrinth seals have been used extensively in industrial production. Better prediction of the performance of a labyrinth seal requires that these mechanisms be understood. This cannot be achieved except by investigating the flowfield details. Therefore, a total variation diminishing (TVD) finite volume scheme is applied to the Navier‐Stokes equations to obtain gas seal flowfield characteristics of axially staggered configuration in this paper. The calculation results here show the evolution process from unsteady flowfield characterization to steady flow pattern. Also, these new flowfield details may provide referable basis for understanding seal mechanisms.

The purpose of this paper is to describe a methodology for predicting the effects of glaze ice geometry on airfoil aerodynamic coefficients by using neural network (NN) prediction. Effects of icing on angle of attack stall are also discussed.

The typical glaze ice geometry covers ice horn leading‐edge radius, ice height, and ice horn position on airfoil surface. By using artificial NN technique, several NNs are developed to study the correlations between ice geometry parameters and airfoil aerodynamic coefficients. Effects of ice geometry on airfoil hinge moment coefficient are also obtained to predict the angle of attack stall.

NN prediction is feasible and effective to study the effects of ice geometry on airfoil performance. The ice horn location and height, which have a more evident and serious effect on airfoil performance than ice horn leading‐edge radius, are inversely proportional to the maximum lift coefficient. Ice accretions on the after‐location of the upper surface of the airfoil leading edges have the most critical effects on the airfoil performance degradation. The catastrophe of hinge moment and unstable hinge moment coefficient can be used to predict the stall effectively.

Since the simulation results of NNs are shown to have high coherence with the tunnel test data, it can be further used to predict coefficients at non‐experimental conditions.

The simulation method by using NNs here can lay the foundation of the further research about the airfoil performance in different ice cloud conditions through predicting the relations between the ice cloud conditions and ice geometry.